1. Field of the Invention
The present invention relates to a semiconductor laser module having a temperature adjustment function which is used in an optical communication, optical information processing, etc.
2. Description of the Related Art
A semiconductor laser module has been widely used as a signal light source for an optical fiber transmission device or the like. Reduction in power consumption has been in progress for transmission devices using optical fibers, and with this progress, it has also been required to reduce the power consumption of circuit boards. Further, with this requirement, reduction in power consumption of various parts installed into circuit boards have been promoted. In connection with the reduction of the power consumption of various parts, particularly reduction in power consumption of semiconductor laser modules has been also required.
Japanese Utility Model Registration Application Laid-open No. Hei-5-8511, Japanese Patent Application Laid-open No. Hei-5-55710, Japanese Patent Application Laid-open No. Hei-5-315696, Japanese Patent Application Laid-open No. Hei-6-169133 and Japanese Patent Application Laid-open No. Hei-7-131106, etc. disclose various semiconductor laser modules which are applied to reduce the power consumption of the semiconductor laser modules. FIG. 1 shows a semiconductor laser module obtained by simplifying the conventional semiconductor laser modules as described above into a simple structure and illustrating it.
As shown in FIG. 1, one end of an optical fiber 32 for transmitting optical signals is accommodated in one side wall of a module package 31 of a semiconductor laser module 30. A temperature adjusting element 33 is disposed on the bottom surface of the inside of the module package 31, and a semiconductor laser 35 and a lens 36 for optically coupling a light beam emitted from the semiconductor laser 35 to the optical fiber 32 are disposed through a base board 34 on the temperature adjusting element 33.
In the semiconductor laser module 30 thus constructed, the following technique is used to reduce the power consumption thereof. The base board 34 on the temperature adjusting element 33 is preferably designed in a compact size, and the base board 34 is preferably formed of a material having a high thermal conductivity so that the temperature adjusting element 33 exhibits a desired cooling capability. However, a material which is not so high in thermal conductivity is used for the base board 36 because the lens 36 is fixed onto the base board 36 by a YAG laser welding method and heat radiation must be suppressed in the YAG laser welding process. That is, it is necessary that a material which is not so high in thermal conductivity is used for the base board 34 to fix the lens 36 onto the base board 34 by the YAG laser welding process although it is better that a material having a high thermal conductivity is used for the base board 34. Therefore, it has been hitherto unavoidable that materials which are not so high in thermal conductivity are used for the base board.
As described above, in the conventional semiconductor laser module structure, in order to reduce the power consumption, that is, enhance the cooling characteristic, materials which are suitable for the YAG laser welding process and are as high in thermal conductivity as possible are used for the base board 34. However, even when the material having the highest thermal conductivity among the materials that are suitable for the YAG laser welding process can be used for the base board 34 in order to improve the heat radiation of the base board 34 between the semiconductor laser 35 and the temperature adjusting element 33 for the lower power consumption, it is impossible to use materials which are higher in thermal conductivity but are not suitable for the YAG laser welding process.